Exercising the gluteal and hamstring muscles correctly and efficiently is difficult and may put strain on the exerciser's knees and back, causing injuries. It is also difficult, if not impossible, to target these muscles without also working out the front of the thighs, which many people do not want to do.
Squats and lunges are two main exercises prescribed to best work out and develop the gluteal and hamstring muscles. Many people cannot perform squats or lunges because of back and knee issues. Squats and lunges are difficult exercises and without proper supervision can cause great harm to knees and backs, especially when using free weights. Proper form is difficult but essential to performing squats and lunges safe and effectively. When doing squats even when supervised it is difficult to keep your body in the proper position and form to be safe and effective. Further, these exercises will always build up quadricep muscles equally with the gluteal and hamstring muscles, if not more at the same time. Many women in particular prefer not to over build their quadriceps but still want to work on their gluteal and hamstring muscles.
When doing squats and lunges, many people let their knees extend forward beyond their toes, which is dangerous for the knees. Professional trainers often provide two points of advice: (a) keep your weight on your heels and (b) don't extend your knees past your toes. People often perform squats and lunges with bar bells or free weights to add more resistance than just their body weight. If not done right the exercises can cause harm to your knees and back.
It is also desirable to have an exercise device that provides the user with the ability to perform different type of exercises, such as core strengthening exercises and leg strengthening exercises.
There is no portable exercise device with built in resistance that is safe and effective, and targeting and isolating the gluteal, hamstring and calf muscles, while removing much of the stress from the knees and back.